HIV-1 protease inhibitors in general have a number of known effects on lipid and carbohydrate metabolism. Our data using both in vivo and in vitro model systems indicate that both indinavir and lopinavir also markedly decrease protein synthesis in skeletal muscle by impairing multiple steps in the control of mRNA translation. The long-term goal of this project is to elucidate the mechanisms by which lopinavir produces myopathy by altering muscle protein balance. The working hypothesis to be tested by the proposed research is that lopinavir antagonizes cell growth signaling systems, that include both eukaryotic initiation factor (elF) 4F and elF2/2B, under both basal conditions and in response to selected anabolic stimuli. Thus, lopinavir alters protein balance by impairing cap-dependent translational control and the formation of the 43S pre-initiation complex. Further, lopinavir adversely effects peptide-chain elongation. To address the questions implicit in our hypothesis, the proposed research has the following Specific Aims: (1) Elucidate the mechanism by which lopinavir impairs elF2B activity in skeletal muscle; (2) Determine whether alterations in the mTOR (mammalian target of rapamycin) nutrient signaling complex are responsible for lopinavir-induced alterations in 4E-BP1 phosphorylation; (3) Determine the mechanism by which lopinavir increases eukaryotic elongation factor (eEF)-2 phosphorylation and whether this change impairs peptide-chain elongation per se; (4) Elucidate the mechanism by which lopinavir impairs the normal anabolic response to nutritional signals (e.g., leucine) in muscle; and (5) Identify the biochemical loci mediating the potentiating effect of zidovudine (AZT) and lamivudine (3TC) on the lopinavir-induced decrease in protein synthesis. Complementary studies using both rats and cultured human myocytes will be used to elucidate the mechanism by which skeletal muscle translation efficiency is reduced by lopinavir, thereby leading to a more complete understanding of the metabolic disturbances produced by this HIV protease inhibitor alone and in combination with other antiretroviral agents. Such data is needed to both realize the full potential and avoid possible pitfalls of this drug in the long-term treatment of HIV-infected individuals. [unreadable] [unreadable] [unreadable]